It is already known that tissue can be destroyed by being subjected to a given "heat dose". At a given temperature, the heat dose is a function of the length of time that heat is applied.
Various means have been proposed for raising temperature, in particular by using infrared radiation or microwave radiation, (see Biodan's U.S. Pat. No. 4,823,812, inventor Eshel).
When using these methods, it is not possible to cause selective heating of the tissue insofar as the radiation is omnidirectional and cannot be focused on a target zone. In addition, these methods are not adapted or are poorly adapted to treating zones of deep tissue. (See the article by Fry entitled "Threshold ultrasonic dosage for structural changes in mammalian brain" published in JASA (1970, 48, 1413-1417)).
To solve this problem, in IEEE Transactions on sonics and ultrasonics, Vol. SE-31, No. 5, September 1984, pp. 473-480, Lizzi et al. propose using soundwaves that are focused to obtain tissue-destroying hyperthermia. As a result, soundwaves of sufficient energy when applied for a sufficiently long period of time serve to reach a "heat dose" threshold required for destroying the target tissue.
The Document WO 89/07909 also describes an apparatus for locating and destroying tumors by ultrasonic hyperthermia.
An apparatus is also known from Document EP-A-0 363 239 for localized destruction of soft structures by means of focused negative elastic pressure waves suitable for giving rise to a cavitation phenomenon in the tissue subjected to the sound. The cavitation phenomenon has the effect of giving rise to localized large mechanical stresses at the cavitation location, thereby destroying the tissue concerned.
When using soundwaves, tissue is generally destroyed by a combination of the cavitation effect and of the heating effect. Unfortunately, the three-dimensional position of where cavitation takes place is difficult to control because cavitation takes place preferentially at the various interfaces encountered by the soundwaves, such as those associated with the skin, with various organs, or with blood vessels. For example, when applying treatment from outside the body as described in EP-A-0 363 239, there is a danger of cavitation phenomena arising anywhere along the path followed by the wave propagating between the transducer and the zone of focus. Given that such cavitation phenomena are destructive, it becomes difficult to control the therapy and to limit it to the target zone.
In addition, the presence of cavitation bubbles on the path of the soundwaves gives rise to a sound screen such that the treatment loses some of its efficiency.
It can thus be seen that it is highly advantageous to minimize the path followed by the sound to reach the focus zone, thus reducing the number of interfaces to be passed through. In other words the transducer is advantageously placed as close as possible to the zone of treatment.
Such closeness also has the advantage of improving the accuracy with which the therapy is applied.
This approach has already been described in Document WO-A-89/07909, FIG. 5, where a rectal probe has been developed for treating tumors of the prostate. The device described is based on using two transducers incorporated in the rectal probe. One serves as a device for observing and locating the prostate, and the other serves to emit waves of ultrasound to perform the therapy.
The therapeutic transducer is coupled to a mirror for reflecting soundwaves. By coupling rotation of the mirror to displacement of the transducer relative to the mirror, it is possible to scan and treat a sector of the prostate. By rotating the assembly, it is possible to treat a given volume of the prostate. The transducer component must be capable of moving very considerably relative to one another in order to make it possible to treat the entire volume of the prostate. This gives rise to a mechanical device that is complex to the detriment of the ease with which it can be used and above all of its accuracy, as is required for this type of therapy.
In addition, that device cannot be used simultaneously to locate and to treat the tumor zone.
Each time a zone is located, it is necessary to displace the observation device to leave room for the treatment device.
A major drawback of this is loss in the accuracy with which treatment is applied, with such loss being due in part to tissue moving when the transducer components are moved. Another major drawback of that device is that progress of the treatment cannot be monitored in real time and the position of the probe cannot be corrected in real time as a function of the results obtained.
An object of the present invention is thus to solve the novel technical problem consisting in providing a solution for destroying tumor tissue (in particular of the prostate), the apparatus being simple to use, accurate, reliable, and capable of simultaneous monitoring in real time.
Another object of the invention is to solve the novel technical problem consisting in providing a solution for destroying tumor tissue (in particular of the prostate) by means of a solution that is sufficiently simple, accurate, and reliable for it to be possible to consider treating tumors (in particular of the prostate) at an early stage, i.e. when the lesions are small in size and thus require observation means and treatment means that are extremely accurate.
Another object of the present invention is to solve the novel technical problem specified above by approaching the tumor tissue via the rectum.
Another object of the present invention is to solve the novel technical problem specified above by approaching the tumor tissue (in particular of the prostate) via the rectum, while simultaneously observing the tumor tissue in real time via endo-cavitary means.
Another object of the present invention is to solve the novel technical problems specified above by adopting a solution that makes it possible to approach the tumor tissue simultaneously via the rectum for the therapeutic device and via endo-cavitary means for the real time observation device.
Another object of the present invention is to solve the novel technical problems specified above by a solution that uses focused ultrasonic soundwaves of short duration and high intensity. In the description and the claims, the term "short duration" is used for periods of exposure to sound that are less than sixty seconds long, in contrast with conventional hyperthermia.
All of these technical problems are solved by the present invention simultaneously, simply, safely, and reliably in a manner that is susceptible of industrial application.